Objective lens driving apparatus and method including visco-elastic support for a magnetic circuit which allows translation of the magnetic circuit without pivoting or rotating there of

ABSTRACT

An objective lens driving apparatus includes a base, an objective lens for converging an optical beam on an optical disc while the optical disc is rotating, and a holding member for holding the objective lens. A first supporting mechanism elastically supports the holding member on the base in such a manner as to allow the holding member to be translated in a focusing direction which is substantially perpendicular to a surface of the optical disc and in a tracking direction which is substantially perpendicular to the focusing direction and parallel to a radial direction of the optical disc. A moving mechanism including a coil and a magnetic circuit for translates the holding member in the focusing direction and the tracking direction by a driving force generated by the coil and the magnetic circuit. A second supporting mechanism for visco-elastically supports the magnetic circuit on the base in such a manner as to translate the magnetic circuit in the focusing direction. The magnetic circuit is translated in an opposite direction to the translation direction of the holding member by a driving force acting oppositely to the driving force for translating the holding member in the focusing direction.

This is a continuation of application Ser. No. 08/315,349, filed on Sep.30, 1994, now U.S. Pat. No. 5,602,808, the entire contents of which arehereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an objective lens driving apparatus,and in particular to an objective lens driving apparatus for use in anoptical disc drive for recording on an optical disc or reproducing datafrom the optical disc while the optical disc is rotating.

2. Description of the Related Art

The above-described type of optical disc drives are provided with anobjective lens driving apparatus for moving an objective lens in afocusing direction and a tracking direction. In this specification, thefocusing direction refers to the direction perpendicular to a surface ofthe optical disc, and the tracking direction refers to a directionhorizontal and parallel to the radial direction of the optical disc.

Briefly referring to FIGS. 13 and 14, a conventional objective lensdriving apparatus 100 will be described. FIG. 13 is a perspective viewof the objective lens driving apparatus 100, and FIG. 14 is a side viewof the objective lens driving apparatus 100. In this specification, thefocusing direction and the tracking direction are set as shown in FIG.13.

As is illustrated in FIGS. 13 and 14, an objective lens 11 is supportedby an objective lens holder 12 in a state where the optical axis thereofis perpendicular to the surface of an optical disc (not shown). In sucha state, the objective lens 11 converges an optical beam on the opticaldisc. The objective lens holder 12 is attached to a carriage 31 via foursprings 13. The four springs 13 support the objective lens holder 12 insuch a manner that the objective lens holder 12 is movable in thefocusing direction and the tracking direction. To the objective lensholder 12, a focusing coil 14 and a tracking coil 15 are attached aswell as the objective lens 11. The focusing coil 14, the tracking coil15, and a pair of magnets 23 are included in an actuator for moving theobjective lens holder 12 in the focusing direction and the trackingdirection. The magnets 23 are attached to a yoke 21 which is fixed tothe carriage 31. The magnets 23 and the yoke 21 are included in amagnetic circuit 26.

The objective lens driving apparatus 100 having the above-describedstructure operates in the following manner.

While the data is recorded on the optical disc or the data is reproducedfrom the optical disc, appropriate focusing servo control and trackingservo control are performed on the actuator. The carriage 31 moves inthe tracking direction by a guiding mechanism and a driving mechanism(not shown), for example, a chassis or a spindle motor.

When a driving current flows through the focusing coil 14, drivingforces F1 and F2 (FIG. 14) are generated and act on the focusing coil 14and the magnetic circuit 26, respectively. The driving forces F1 and F2have the same magnitude and act in opposite directions from each other.The driving force F1 moves the objective lens holder 12 in the focusingdirection and is conveyed to the carriage 31 via the springs 13, therebyvibrating the carriage 31. The driving force F2 vibrates the yoke 21 ofthe magnetic circuit 26 and the carriage 31 on which the yoke 21 isfixed.

The vibration of the carriage 31 caused by the driving forces F1 and F2is conveyed to the optical disc through the guiding mechanism and thedriving mechanism. If such a path for conveying the vibration has aspecific resonance point, focusing servo control is impossible. Such aproblem, which occurs more easily and more frequently today when lessrigid components are used in the optical disc drives in order to reducethe size and weight of the drives, is a barrier against furtherreduction in the size and weight of the drives.

Japanese Laid-Open Patent Publication No. 4-32035 proposes, as one ofthe solutions of such a problem, insertion of a visco-elastic body suchas rubber or a spring into the conveying path of the vibration in orderto damp the vibration. Such a method has problems in that, for example,positioning precision of the components of the objective lens drivingapparatus is lowered. Especially the method, described in theabove-mentioned publication, of visco-elastically supporting themagnetic circuit by rubber or a cantilever spring tends to presentproblems in that sufficient damping is not obtained, and in that themagnetic circuit is inclined by the movement of the objective lensholder and thus contacts the coil.

Japanese Laid-Open Patent Publication No. 4-245033 proposes provision ofa device for generating a vibration having the same magnitude with andthe opposite phase to the vibration generated by the movement of theobjective lens holder in order to counteract the vibration. Provision ofsuch a device increases the number of the components and the size of theapparatus.

SUMMARY OF THE INVENTION

One aspect of the present invention relates to an objective lens drivingapparatus including a base; an objective lens for converging an opticalbeam on an optical disc while the optical disc is rotating; a holdingmember for holding the objective lens; a first supporting mechanism forelastically supporting the holding member on the base in such a manneras to allow the holding member to be translated in a focusing directionwhich is substantially perpendicular to a surface of the optical discand in a tracking direction which is substantially perpendicular to thefocusing direction and parallel to a radial direction of the opticaldisc; a moving mechanism including a coil and a magnetic circuit fortranslating the holding member in the focusing direction and thetracking direction by a driving force generated by the coil and themagnetic circuit; and a second supporting mechanism forvisco-elastically supporting the magnetic circuit on the base in such amanner as to translate the magnetic circuit in the focusing direction.The magnetic circuit is translated in an opposite direction to thetranslation direction of the holding member by a driving force actingoppositely to the driving force for translating the holding member inthe focusing direction.

Another aspect of the present invention relates to an objective lensdriving apparatus including a base; an objective lens for converging anoptical beam on an optical disc while the optical disc is rotating; aholding member for holding the objective lens; a first supportingmechanism for elastically supporting the holding member on the base insuch a manner as to allow the holding member to be translated in afocusing direction which is substantially perpendicular to a surface ofthe optical disc and in a tracking direction which is substantiallyperpendicular to the focusing direction and parallel to a radialdirection of the optical disc; a moving mechanism including a coil and amagnetic circuit for translating the holding member in the focusingdirection and the tracking direction by a driving force generated by thecoil and the magnetic circuit; and a second supporting mechanism forvisco-elastically supporting the magnetic circuit on the base in such amanner as to vibrate the magnetic circuit in the focusing direction atthe lowest resonance frequency thereof. The magnetic circuit istranslated in an opposite direction to the translation direction of theholding member by a driving force acting oppositely to the driving forcefor translating the holding member in the focusing direction.

Thus, the invention described herein makes possible an advantage ofproviding an objective lens driving apparatus in which vibrationgenerated by the movement of an objective lens holder in the focusingdirection and the tracking direction can be effectively restrictedwithout causing a magnetic circuit to contact a coil, or withoutincreasing the number of components or the size of the objective lensdriving apparatus.

This and other advantages of the present invention will become apparentto those skilled in the art upon reading and understanding the followingdetailed description with reference to the accompanying figures.

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not limitativeof the present invention, and wherein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an objective lens driving apparatus in afirst exemplary embodiment of the present invention;

FIG. 2 is a side view of the objective lens driving apparatus shown inFIG. 1;

FIG. 3 is a perspective view of an objective lens driving apparatus in asecond exempalary embodiment of the present invention;

FIG. 4 is a perspective view of an objective lens driving apparatus in athird exemplary embodiment of the present invention;

FIG. 5 is a side view of the objective lens driving apparatus shown inFIG. 4;

FIG. 6 is a perspective view of an objective lens driving apparatus in afourth exemplary embodiment of the present invention;

FIG. 7 is a perspective view of an objective lens driving apparatus in afifth exemplary embodiment of the present invention;

FIG. 8 is a side view of the objective lens driving apparatus shown inFIG. 7;

FIG. 9 is a partial top view of an objective lens driving apparatus in asixth exemplary embodiment of the present invention;

FIG. 10 is an exploded perspective view of an objective lens drivingapparatus in a seventh exemplary embodiment of the present invention;

FIGS. 11 and 12 are each a graph illustrating the transfer function ofthe vibration of a mounting plate with respect to the vibration of anobjective lens holder in the objective lens driving apparatus shown inFIG. 10 and in a conventional objective lens driving apparatus;

FIG. 13 is a perspective view of a conventional objective lens drivingapparatus; and

FIG. 14 is a side view of the conventional objective lens drivingapparatus shown in FIG. 13.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the present invention will be described by way ofillustrative examples with reference to the accompanying drawings.

(Example 1)

With reference to FIGS. 1 and 2, an objective lens driving apparatus 1in a first exemplary embodiment of the present invention will bedescribed. FIG. 1 is a perspective view of the objective lens drivingapparatus 1, and FIG. 2 is a side view of the objective lens drivingapparatus 1.

As is illustrated in FIGS. 1 and 2, an objective lens 11 is supported byan objective lens holder 12 in a state where the optical axis thereof isperpendicular to a surface of an optical disc (not shown). In such astate, the objective lens 11 converges an optical beam onto the opticaldisc. The objective lens holder 12 is attached to a carriage 31 actingas a base via four springs 13 acting as first supporting means eachformed of an elastic wire. The four springs 13 allow the objective lensholder 12 to move mainly in the focusing direction and the trackingdirection. The carriage 31 includes a horizontal portion 31b andvertical portions 31a and 31c each extended perpendicularly from therespective ends of the horizontal portion 31b. Thus, the carriage 31 hasa substantially C-shaped vertical cross section. The four springs 13 areeach fixed at both ends thereof to the surface of the vertical portion31a opposed to the vertical portion 31c and a vertical portion 12b (FIG.2) of the objective lens holder 12. A mirror 10 for guiding the opticalbeam emitted from an optical source (not shown) to be incident on theobjective lens 11 is located on the horizontal portion 31b.

As is shown in FIG. 2, the objective lens holder 12 includes a lensretaining portion 12a in which the objective lens 12 is fixed and thevertical portion 12b. A focusing coil 14 is fixed on a surface of thevertical portion 12b opposed to the vertical portion 31c, and a trackingcoil 15 is fixed on the focusing coil 14. The focusing coil 14, thetracking coil 15 and the objective lens holder 12 are included in amovable section 25. The focusing coil 14, the tracking coil 15 and amagnetic circuit 26 are included in an actuator for moving the objectivelens holder 12 in the focusing direction and the tracking direction.

The magnetic circuit 26 includes a pair of magnets 23 located so as tointerpose the tracking coil 15 and also includes a yoke 21 on which themagnets 23 are fixed. One of the magnets 23 is inserted into thefocusing coil 14. The yoke 21 is visco-elastically supported on thecarriage 31 by a pair of leaf springs 22 acting as second supportingmeans.

The leaf springs 22 are fixed at both ends thereof to the verticalportion 31c and the yoke 21 in the state where main surfaces thereof arehorizontal and parallel to each other in the focusing direction. Theleaf springs 22 are attached to a top end and a bottom end of the yoke21, respectively. Preferably, the leaf springs 22 are attached to themagnetic circuit 26 in such a manner that the supporting center of theleaf springs 22 corresponds with the center of gravity of the magneticcircuit 26. The leaf springs 22 have substantially the same elasticconstant.

The objective lens driving apparatus 1 having the above-describedstructure operates in the following manner.

When a driving current flows through the focusing coil 14, a drivingforce F1 acting in the focusing direction is generated. The drivingforce F1 translates the objective lens holder 12 in the focusingdirection. Simultaneously, a driving force F2 equal in magnitude withand opposite in acting direction to the driving force F1 is generated.The driving force F2 translates the magnetic circuit 26 in the oppositedirection to the translation direction of the objective lens holder 12without pivoting the magnetic circuit 26 toward the vertical portion31c. The pivoting movement of the magnetic circuit 26 is substantiallyprohibited by the leaf springs 22 arranged parallel to each other in thefocusing direction.

The translation of the magnetic circuit 26 in the opposite direction tothe translation direction of the objective lens holder 12 counteractsthe vibration generated by the movement of the objective lens holder 12in the focusing direction. Accordingly, the vibration caused by themovement of the objective lens holder 12 in the focusing direction canbe significantly reduced. As a result, a stable focusing servo controlcan be realized.

Further, as is described above, the leaf springs 22 are arrangedparallel to each other in the focusing direction. As a result, themagnetic circuit 26 is substantially prohibited from pivoting toward thevertical portion 31c while being translated oppositely to the objectivelens holder 12 in the focusing direction. For this reason, the yoke 21and the magnets 23 are kept out of contact with the focusing coil 14 andthe tracking coil 15. Accordingly, the distance between the magneticcircuit 26 and each of the coils 14 and 15 can be set at a minimumpossible distance. Such a short distance is advantageous in reducing thetotal size of the objective lens driving apparatus 1.

The leaf springs 22 are formed of, for example, phosphorus bronze,beryllium bronze, or stainless steel. Phosphorus bronze is lessexpensive than the other materials. Beryllium bronze and stainless steelare high in resistance against wearing and corrosion, respectively. Theleaf springs 22 formed of one of the above-mentioned materials arestrong against deformation during assembly of the objective lens drivingapparatus 1, and the characteristics thereof are not changed much inaccordance with the temperature.

As is described above, the leaf springs 22 are preferably located insuch a position that the supporting center of the leaf springs 22corresponds with the center of gravity of the magnetic circuit 26. Evenif the supporting center of the leaf springs 22 is offset from thecenter of gravity of the magnetic circuit 26, the vibration conveyed tothe carriage 31 for the lack of counteraction due to such positionaloffset presents no problem as long as the vibration is too small tocause any trouble in performing focusing servo control.

In the first example, a pair of leaf springs 22 are provided forvisco-elastically supporting the magnetic circuit 26 in the state wherethe main surfaces thereof are arranged parallel to each other in thefocusing direction. In such a structure, since the leaf springs 22 arehighly rigid against deformation in all directions except for thedirection perpendicular to the main surfaces thereof, namely, thefocusing direction, the leaf springs 22 are untwisted even when exposedto the driving force F2. In other words, the magnetic circuit 26vibrates at the lowest resonance frequency thereof in the focusingdirection. Thus, the magnetic circuit 26 is not inclined in anydirection. Accordingly, the magnetic circuit 26 is kept out of contactwith the coils 14 and 15, which allows the distance between the magneticcircuit 26 and each of the coils 14 and 15 to be set at a minimumpossible distance. This is advantageous in reducing the total size ofthe objective lens driving apparatus 1.

(Example 2)

With reference to FIG. 3, an objective lens driving apparatus 2 in asecond exemplary embodiment of the present invention will be described.FIG. 3 is a perspective view of the objective lens driving apparatus 2.Identical elements with those in the first example will bear identicalreference numerals therewith, and explanation thereof will be omitted.

In the second example, a pair of hinges 122 are provided forvisco-elastically supporting the magnetic circuit 26 instead of the pairof leaf springs 22. The hinges 122 are each a plate having two V-shapedgrooves on a main surface thereof. The hinges 122 are attached to thevertical portion 31c in the state where the surfaces thereof having theV-grooves are horizontal and parallel to each other one above the other.Further, the surfaces of the hinges 122 having the V-shaped grooves areopposed to each other. Since the hinges 122 function in the same way asthe leaf springs 22, the objective lens driving apparatus 2 operates inthe same manner as the objective lens driving apparatus 1. Thus, thevibration caused by the movement of the objective lens holder 12 in thefocusing direction is significantly reduced by counteraction.

As is described above, the surfaces of the hinges 122 having theV-shaped grooves are arranged parallel to each other one above theother. By such arrangement, the reaction force of the hinges 122 isgenerated in the focusing direction. Accordingly, the magnetic circuit26 is prohibited from pivoting toward the vertical portion 31c whilebeing translated oppositely to the objective lens holder 12. For thisreason, the yoke 21 and the magnets 23 are kept out of contact with thefocusing coil 14 and the tracking coil 15. This allows the distancebetween the magnetic circuit 26 and each of the coils 14 and 15 to beset at a minimum possible distance. As a result, the objective lensdriving apparatus 2 can be reduced in size, while greatly reducing thevibration of the carriage 31 caused by the movement of the objectivelens holder 12 in the focusing direction.

The hinges 122 are formed of, for example, a resin such as thermoplasticpolyester elastomer, which is high in resistance against wearing. Thehinges 122 formed of a resin, which can be produced by molding, are easyto mass-produce. The hinges 122 formed of a resin can be moldedintegrally with the vertical portion 31c or a member for attaching thehinges 122 to the yoke 21. Since there is little possibility that thehinges 122 formed of a resin might be deformed during the assembly, theassembly of the objective lens driving apparatus 2 can be performed moreeasily and at a higher yield.

As in the first example, the hinges 122 are preferably located in such amanner that the supporting center of the hinges 122 corresponds with thecenter of gravity of the magnetic circuit 26. Such correspondence is notabsolutely necessary as long as the vibration conveyed to the carriage31 for the lack of counteraction due to such positional offset is toosmall to cause any trouble in performing focusing servo control.

In the second example, a pair of hinges 122 are provided forvisco-elastically supporting the magnetic circuit 26 in the state wherethe surfaces thereof having the V-shape grooves are parallel to eachother one above the other. In such a structure, since the hinges 122 arehighly rigid against deformation in all directions except for thedirection perpendicular to the surfaces thereof having the V-shapedgrooves, namely, the focusing direction, the hinges 122 are untwistedeven when exposed to the driving force F2. In other words, the magneticcircuit 26 vibrates at the lowest resonance frequency thereof in thefocusing direction. Thus, the magnetic circuit 26 is not inclined in anydirection. Accordingly, the magnetic circuit 26 is kept out of contactwith the coils 14 and 15, which allows the distance between the magneticcircuit 26 and each of the coils 14 and 15 to be set at a minimumpossible distance. This is advantageous in reducing the total size ofthe objective lens driving apparatus 2.

(Example 3)

With reference to FIGS. 4 and 5, an objective lens driving apparatus 3in a third examplary embodiment of the present invention will bedescribed. FIG. 4 is a perspective view of the objective lens drivingapparatus 3, and FIG. 5 is a side view of the objective lens drivingapparatus 3. Identical elements with those in the first example willbear identical reference numerals therewith, and explanation thereofwill be omitted.

In the third example, two pairs of elastic wires 222a and 222b areprovided for visco-elastically supporting the magnetic circuit 26. Theupper pair of wires 222a are attached to top corners of the yoke 21, andthe lower pair of wires 222b (only one wire is shown in FIG. 4) areattached to the bottom corners of the yoke 21. All the four wires 222aand 222b are horizontal. The distance between the wires 222a and thedistance between the wires 222b are each expanded from the yoke 21toward the vertical portion 31c of the carriage 31. Since the pairs ofwires 222a and 222b function in the same manner as the leaf springs 22,the objective lens driving apparatus 3 operates in the same way as theobjective lens driving apparatus 1. Thus, the vibration caused by themovement of the objective lens holder 12 in the focusing direction issignificantly reduced by counteraction.

As is appreciated from FIGS. 4 and 5, the elastic wires 222a and 222bare located in such a manner that the reaction force of the elasticwires 222a and 222b is generated in the focusing direction. Accordingly,the magnetic circuit 26 is substantially prohibited from pivoting towardthe vertical portion 31c while being translated oppositely to theobjective lens holder 12 in the focusing direction. For this reason, theyoke 21 and the magnets 23 are kept out of contact with the focusingcoil 14 and the tracking coil 15. This allows the distance between themagnetic circuit 26 and each of the coils 14 and 15 to be set at aminimum possible distance. As a result, the objective lens drivingapparatus 3 can be reduced in size.

The elastic wires 222a and 222b are preferably formed of, for example,phosphorus bronze, beryllium bronze, or stainless steel. By using one ofsuch materials, the magnetic circuit can be easily designed to vibratein the focusing direction at a lower resonance frequency. The elasticwires 222a and 222b formed of one of such materials are advantageous inbeing less influenced by temperature as well as in effectively absorbingthe vibration.

In the third example, two pairs of elastic wires 222a and 222b areprovided for visco-elastically supporting the magnetic circuit 26. Insuch a structure, the assembly of the elastic wires 222a and 222b ishighly rigid against deformation in all directions except for thedirection perpendicular to a plane defined by the elastic wires 222a anda plane defined by the elastic wires 222b. Namely, the assembly of theelastic wires 222a and 222b is highly rigid against deformation in alldirections except for the focusing direction. In other words, themagnetic circuit 26 vibrates at the lowest resonance frequency thereofin the focusing direction. Accordingly, the magnetic circuit 26 is notinclined in any direction. Thus, the magnetic circuit 26 is kept out ofcontact with the coils 14 and 15, which allows the distance between themagnetic circuit 26 and each of the coils 14 and 15 to be set at aminimum possible distance. As a result, the total size of the objectivelens driving apparatus 3 can be reduced.

(Example 4)

With reference to FIG. 6, an objective lens driving apparatus 4 in afourth exemplary embodiment of the present invention will be described.FIG. 6 is a perspective view of the objective lens driving apparatus 4.Identical elements with those in the first example will bear identicalreference numerals therewith, and explanation thereof will be omitted.

In the fourth example, two pairs of elastic wires 322 forvisco-elastically supporting the magnetic circuit 26 are providedparallel to one another. Due to such a structure, the magnetic circuit26 is translated in the tracking direction as well as in the focusingdirection with no pivoting movement. Accordingly, the vibration causedby the movement of the objective lens holder 12 in the focusingdirection and also the vibration caused by the movement of the objectivelens holder 12 in the tracking direction can be counteracted by thevibration of the magnetic circuit 26, thereby significantly reducingboth types of vibration.

The elastic wires 322 are preferably formed of, for example, phosphorusbronze, beryllium bronze, or stainless steel. By using one of suchmaterials, the magnetic circuit can be easily designed to vibrate in thefocusing direction at a lower resonance frequency. The elastic wires 322formed of one of such materials are advantageous in being lessinfluenced by temperature as well as in effectively absorbing thevibration.

In the fourth example, the effects obtained in the third example canalso be obtained.

(Example 5)

With reference to FIGS. 7 and 8, an objective lens driving apparatus 5in a fifth exemplary embodiment of the present invention will bedescribed. FIG. 7 is a perspective view of the objective lens drivingapparatus 5, and FIG. 8 is a side view of the objective lens drivingapparatus 5. Identical elements with those in the first example willbear identical reference numerals therewith, and explanation thereofwill be omitted.

In the fifth example, as is shown in FIGS. 7 and 8, a leaf spring 54fixed to the vertical portion 31c of the carriage 31 visco-elasticallysupports the magnetic circuit 26 via a slidable member 50, instead ofdirectly supporting the yoke 21 of the magnetic circuit 26. The slidablemember 50 is attached to the yoke 21 on the other side from the coils 14and 15. The leaf spring 54 has a sawtooth-like cross section. Theslidable member 50 has two holes through which a pair of guide posts 52are extended vertically with respect to the horizontal portion 31b,namely, substantially in the focusing direction. The leaf spring 54visco-elastically supports the slidable member 50 so as to allow theslidable member 50 to slide in the direction in which the guide posts 52are extended.

By providing the slidable member 50 and the guide posts 52 in theabove-described manner, the magnetic circuit 26 is movable only in thedirection parallel to the extending direction of the guide posts 52,namely, in the focusing direction. Accordingly, it is not necessary tolocate the leaf spring 54 in such a manner as to prohibit the pivotingmovement of the magnetic circuit 26 toward the vertical portion 31c. Theleaf spring 54 may be replaced with a flat leaf spring as used in thefirst example or a hinge as used in the second example. However, it isnot necessary to provide a pair of leaf springs or a pair of hinges. Inthe case that elastic wires are provided as in the third example insteadof the leaf spring 54, it is sufficient to provide only a pair of wiresat the same height from the horizontal portion 31b instead of two pairsof wires.

The shape of the leaf spring 54 is not limited to the one shown in FIGS.7 and 8. The leaf spring 54 may have any shape as long as an elasticforce for moving the slidable member 50 in the focusing direction isgenerated.

In the fifth example also, the magnetic circuit 26 vibrates at thelowest resonance frequency thereof in the focusing direction. Since thepivoting movement of the magnetic circuit 26 is substantially prohibitedby the combination of the slidable member 50 and the guide posts 52, themagnet 23 and the yoke 21 of the magnetic circuit 26 are kept out ofcontact with the focusing coil 14 and the tracking coil 15.

(Example 6)

With reference to FIG. 9, an objective lens driving apparatus 6 in asixth exemplary embodiments of the present invention will be described.FIG. 9 is a partial top view of the objective lens driving apparatus 6.

As is shown in FIG. 9, the magnetic circuit 26 is visco-elasticallysupported by three elastic wires 61, 62 and 63. The elastic wires 61, 62and 63 have an identical length and are located at the same height fromthe horizontal portion 31b of the carriage 31. A vertical portion 31c'of the carriage 31 has a substantially C-shaped horizontal cross sectionincluding two extended portions 34 and a central portion 35. Ends of thewires 61 and 63 are attached to ends of the extended portions 34,respectively. An end of the wire 62 is attached to the central portion35. The other end of the wire 62 is attached to a surface of the yoke 21opposed to the vertical portion 31c'. The other ends of the wires 61 and63 are respectively attached to attaching members which are located onside surfaces of the yoke 21 extended perpendicular to the trackingdirection. In such a structure, the same effects as in the previous fiveexamples can be obtained.

(Example 7)

With reference to FIG. 10, an objective lens driving apparatus 7 in aseventh exemplary embodiment of the present invention will be described.FIG. 10 is an exploded perspective view of the objective lens drivingapparatus 7.

In the seventh example, the carriage 31 has a receptacle portion 36surrounded by side portions 31c" and 31a" and connecting portions 32b".The side portions 31c" and 31a" respectively correspond to the verticalportions 31c and 31a in the first through fifth examples. The magneticcircuit including the yoke 21 and a pair of magnets (not shown) fixed tothe yoke 21 is attached to one of the connecting portions 32b".

As is illustrated in FIG. 10, the objective lens holder 12 forsupporting the objective lens 11 is attached to a spring holder 16 bythe four springs 13 in such a manner that the objective lens holder 12can be translated in the focusing direction and the tracking direction.The spring holder 16 is accommodated in the receptacle portion 36 of thecarriage 31 together with the objective lens holder 12, a focusing coiland a tracking coil (neither is shown) both fixed on the objective lensholder 12, and the like.

The yoke 21 is supported in a receptacle portion 36 of the carriage 31by two leaf springs 22 arranged parallel to each other in the focusingdirection and perpendicular to the springs 13. The magnetic circuit, thefocusing coil and the tracking coil are included in an actuator fortranslating the objective lens holder 12 in the focusing direction andthe tracking direction. The leaf springs 22 are located in the samemanner as in the first example except being attached to the connectingportion 32b". Accordingly, the magnetic circuit 26 vibrates in thefocusing direction at the lowest resonance frequency thereof.

The carriage 31 is attached to a mounting plate (not shown) via a pairof guide shafts 32 extended in the tracking direction. The mountingplate includes a spindle motor for rotating the optical disc and isattached to a chassis of the objective lens driving apparatus 7 via adamping material.

FIG. 11 is a graph illustrating the transfer function of the vibrationof the mounting plate with respect to the vibration of the objectivelens holder 12 in the objective lens driving apparatus 7 in the seventhexample and in a conventional objective lens driving apparatus. In theconventional objective lens driving apparatus, the magnetic circuit isattached to the carriage directly. In the objective lens drivingapparatus 7, the total mass of the objective lens 11 and the objectivelens holder 12 is approximately 200 mg, the mass of the magnetic circuitis approximately 500 mg, and the mass of the mounting plate isapproximately 150 g. A first spring-mass system including the objectivelens holder 12, the four springs 13, and the like is adjusted to have alowest resonance frequency of vibration in the focusing direction ofapproximately 60 Hz, and the damping ratio is adjusted to beapproximately 0.01. A second spring-mass system including the magneticcircuit and the leaf springs 22 is adjusted to have a lowest resonancefrequency of vibration in the focusing direction of approximately 65 Hz,and the damping ratio is adjusted to be approximately 0.01. The mountingplate is adjusted to have a lowest resonance frequency of approximately100 Hz and a damping ratio of approximately 0.1 by selection of anappropriate damping material.

As is appreciated from FIG. 11, the vibration of the mounting plate isless in the objective lens driving apparatus 7 than in the conventionalapparatus by approximately 60 dB at a frequency of 1 kHz.

Here, the lowest resonance frequency of vibration of the secondspring-mass system, namely, the lowest resonance frequency of vibrationof the magnetic circuit is adjusted to be 65 Hz, which is proximate tothe lowest resonance frequency of vibration (60 Hz) of the firstspring-mass system in the focusing direction, namely, the lowestresonance frequency of the vibration of the movable section in thefocusing direction. By setting the former proximate to the latter, thevibration caused by the movement of the movable section in the focusingdirection is counteracted more effectively.

If it is difficult to set the lowest resonance frequency of vibration ofthe magnetic circuit proximately to the lowest resonance frequency ofvibration of the movable section, the former may be set at half or lessof the frequency of the vibration which is to be reduced. In this way,the vibration caused by the movement of the movable section in thefocusing direction is sufficiently alleviated to prevent any trouble inperforming focusing servo control.

FIG. 12 is a graph illustrating the transfer function of the vibrationof the mounting plate with respect to the vibration of the objectivelens holder 12 in the objective lens driving apparatus 7 and in theconventional apparatus. In the objective lens driving apparatus 7, thelowest resonance frequency of vibration of the second spring-mass systemis set at 500 Hz while the frequency of the vibration to be reduced is 1kHz. As is appreciated from FIG. 12, the vibration of the mounting plateis less in the objective lens driving apparatus 7 than in theconventional apparatus by approximately 10 dB at the frequency of 1 kHz.

If the conveying path of the vibration has a specific resonance point inthe vicinity of the resonance frequency, the lowest resonance frequencyof vibration of the magnetic circuit is preferably set at a level as faras possible from the resonance point and lower than the frequency of theresonance point.

An objective lens driving apparatus according to the present inventionis not limited to those described in the first through the seventhexamples. For example, a plurality of magnetic circuits may be provided,in which case, each of the magnetic circuits is adjusted to vibrate atthe lowest resonance frequency thereof in the focusing direction. Thesame effects can be obtained.

In the first through fourth, sixth and seventh exemplary embodiment, bysubstantially equalizing the height of members for visco-elasticallysupporting the magnetic circuit, such as the leaf springs 22 or thehinges 122, from the horizontal portion 31b of the carriage 31 with theheight of the springs 13 for elastically supporting the objective lensholder 12 from the horizontal portion 31b, an increase in the totalthickness of the objective lens driving apparatus can be avoided despitethe provision of the members for visco-elastically supporting themagnetic circuit. In the fifth exemplary embodiment also, by equalizingthe height of the guide posts with the height of the springs 13 from thehorizontal portion 31b, an increase in the total thickness of theobjective lens driving apparatus can be avoided.

As has been described so far, an objective lens driving apparatusaccording to the present invention includes a mechanism forvisco-elastically supporting the magnetic circuit in such a manner as tovibrate the magnetic circuit at substantially the lowest resonancefrequency thereof in the focusing direction. Such a mechanism supportsthe magnetic circuit so as to allow the magnetic circuit to betranslated in the focusing direction without pivoting. Due to such astructure, when the objective lens holder moves in the focusingdirection, the magnetic circuit is translated oppositely to theobjective lens holder. Thus, the vibration caused by the movement of theobjective lens holder in the focusing direction can be counteracted. Asa result, problems such as the impossibility of focusing servo controlis prevented, which realizes stable focusing servo control.

According to the present invention, since an apparatus for counteractingthe vibration as required in conventional apparatuses is eliminated, thenumber of components can be reduced and the total size of the drivingapparatus can be decreased.

Since the pivoting movement of the magnetic circuit is substantiallyprohibited by the mechanism for visco-elastically supporting themagnetic circuit, the magnetic circuit can be kept out of contact withthe focusing coil and the tracking coil when the magnetic circuit movesin the focusing direction. Such an advantage allows the distance betweenthe magnetic circuit and the coils to be set at a minimum possibledistance, which reduces the total size of the objective lens drivingapparatus.

By locating the mechanism for visco-elastically supporting the magneticcircuit at substantially the same height as the height at which themember for supporting the objective lens holder is located, an increasein the total thickness of the objective lens driving apparatus can beavoided.

By substantially equalizing the lowest resonance frequency of vibrationof the magnetic circuit, namely, the resonance frequency of vibration ofthe magnetic circuit in the focusing direction to the resonancefrequency of vibration of the movable section including the objectivelens holder in the focusing direction, the undesirable vibration causedby the movement of the objective lens holder in the focusing directioncan be counteracted and reduced more effectively. Even if the above tworesonance frequencies cannot be substantially the same, the undesirablevibration can still be alleviated by setting the lowest resonancefrequency of vibration of the magnetic circuit at 1/2 or less of thefrequency of vibration which is to be reduced.

Various other modifications will be apparent to and can be readily madeby those skilled in the art without departing from the scope and spiritof this invention. Accordingly, it is not intended that the scope of theclaims appended hereto be limited to the description as set forthherein, but rather that the claims be broadly construed.

What is claimed is:
 1. An objective lens driving apparatus, comprising:abase; an objective lens for converging an optical beam onto an opticaldisc while the optical disc is rotating; holding means for holding saidobjective lens; first supporting means attached to one side wall of saidbase for elastically supporting said holding means on said base in sucha manner as to allow said holding means to be translated in a focusingdirection which is substantially perpendicular to a surface of theoptical disc and in a tracking direction which is substantiallyperpendicular to the focusing direction and parallel to a radialdirection of the optical disc; moving means including a coil and amagnetic circuit for translating said holding means in the focusingdirection and the tracking direction by a driving force generated bysaid coil and said magnetic circuit; and second supporting meansattached to another side wall of said base for visco-elasticallysupporting said magnetic circuit on said base in such a manner as totranslate said magnetic circuit in the focusing direction, wherein saidmagnetic circuit is translated in an opposite direction without rotatingsaid magnetic circuit to the translation direction of said holding meansby a driving force acting oppositely to the driving force fortranslating said holding means in the focusing direction.
 2. Anobjective lens driving apparatus according to claim 1, wherein saidsecond supporting means includes a plurality of elastic members forgenerating an elastic force in a direction parallel to the focusingdirection.
 3. An objective lens driving apparatus according to claim 2,wherein said plurality of elastic members are a plurality of leafsprings each of which is located so as to have a main surface thereofperpendicular with respect to said focusing direction.
 4. An objectivelens driving apparatus according to claim 3, wherein the plurality ofleaf springs are each formed of a material selected from the groupconsisting of phosphorus bronze, beryllium bronze, and stainless steel.5. An objective lens driving apparatus according to claim 2, wherein theplurality of elastic members are a plurality of hinges, each of which islocated so as to have a main surface thereof in a vertical state withrespect to the focusing direction.
 6. An objective lens drivingapparatus according to claim 5, wherein said plurality of hinges areeach formed of a thermoplastic resin.
 7. An objective lens drivingapparatus according to claim 2, wherein said plurality of elasticmembers is a plurality of wires located parallel to one another.
 8. Anobjective lens driving apparatus according to claim 7, wherein saidplurality of wires are each formed of a material selected from the groupconsisting of phosphorus bronze, beryllium bronze, and stainless steel.9. An objective lens driving apparatus according to claim 7, whereinsaid plurality of wires are two pairs of wires.
 10. An objective lensdriving apparatus according to claim 2, wherein said plurality ofelastic members are positioned perpendicular to both the focusingdirection and the tracking direction.
 11. An objective lens drivingapparatus according to claim 1, wherein said magnetic circuit vibratesat a lowest resonance frequency thereof in said focusing direction, andsaid lowest resonance frequency is substantially equal to a lowestresonance frequency of vibration of a movable section in the focusingdirection, said movable section including said objective lens, saidholding means and said coil.
 12. An objective lens driving apparatusaccording to claim 1, wherein said magnetic circuit vibrates at a lowestresonance frequency thereof in said focusing direction, and said lowestresonance frequency is no greater than half of said frequency ofvibration which is to be reduced.
 13. An objective lens drivingapparatus according to claim 1, wherein, said first supporting means andsaid second supporting means are located at an identical height witheach other.
 14. An objective lens driving apparatus according to claim1, wherein a supporting center of said second supporting meanscorresponds with a center of gravity of said magnetic circuit.
 15. Anobjective lens driving apparatus according to claim 1, wherein at leastpart of said second supporting means is positioned above a lower edge ofsaid magnetic circuit.
 16. An objective lens driving apparatus accordingto claim 1, wherein said second supporting means prevents said magneticcircuit from pivoting.
 17. An objective lens driving apparatus accordingto claim 1, wherein said second supporting means is positioned outsideof a conveying path of the translation of said magnetic circuit.
 18. Anobjective lens driving apparatus according to claim 1, wherein saidsecond supporting means only allows said magnetic circuit to moveparallel to the focusing direction.
 19. A method of maintainingseparation between a magnetic circuit and a coil in an optical diskdrive comprising the steps of:holding an objective lens for convergingan optical beam onto an optical disc in a holder; elastically supportingsaid holder on a base including allowing said holder to be translated ina focusing direction which is substantially perpendicular to a surfaceof the optical disc and in a tracking direction which is substantiallyperpendicular to said focusing direction and parallel to a radialdirection of the optical disc by first supporting means which isattached to one side wall of said base; generating a driving force insaid coil and said magnetic circuit; translating said holder in saidfocusing direction and said tracking direction in response to saiddriving force; visco-elastically supporting said magnetic circuit onsaid base in a direction parallel to said tracking direction by secondsupporting means which is attached to another side wall of said base;and preventing pivoting by said visco-elastically supporting step ofsaid magnetic circuit while said magnetic circuit is being translated ina direction opposite said focusing direction, thereby maintaining theseparation between said magnetic circuit and said coil.
 20. A methodaccording to claim 19, further comprising vibrating said magneticcircuit at a lowest resonance frequency thereof in said focusingdirection, wherein said lowest resonance frequency is substantiallyequal to a lowest resonance frequency of vibration of a movable sectionin said focussing direction, said movable section including saidobjective lens, said holder and said coil.
 21. A method according toclaim 19, further comprising vibrating said magnetic circuit at a lowestresonance frequency which is no greater than half of a lowest resonancefrequency of vibration of a movable section in said focussing direction,said movable section including said object lens, said holder and saidcoil.
 22. An objective lens driving apparatus, comprising:a base; anobjective lens for converging an optical beam onto an optical disc whilethe optical disc is rotating; holding means for holding said objectivelens; first supporting means attached to one side wall of said base forelastically supporting said holding means to said base in such a manneras to allow said holding means to be moved with a substantiallytranslational motion in a focusing direction which is substantiallyperpendicular to a surface of the optical disc and in a trackingdirection which is substantially perpendicular to the focusing directionand parallel to a radial direction of the optical disc; moving meansincluding a coil and a magnetic circuit for moving said holding means inthe focusing direction and in the tracking direction by a driving forcegenerated by said coil and said magnetic circuit; and second supportingmeans attached to another side wall of said base for visco-elasticallysupporting said magnetic circuit on said base in such a manner as tolimit the movement of said magnetic circuit to a substantially linearmovement with substantially translational motion in the focusingdirection, wherein said magnetic circuit is moved linearly withsubstantially translational motion in a direction opposite the directionof motion of said holding means by a driving force acting in a directionopposing the driving force moving said holding means in the focusingdirection.
 23. An objective lens driving apparatus according to claim22, wherein said second supporting means includes a plurality of membersaligned only in said focusing direction.
 24. An objective lens drivingapparatus, comprising:a base; an objective lens for converging anoptical beam onto an optical disc while the optical disc is rotating;holding means for holding said objective lens; first supporting meansattached to one side wall of said base for elastically supporting saidholding means on said base in such a manner as to allow said holdingmeans to be translated in a focusing direction which is substantiallyperpendicular to a surface of the optical disc and in a trackingdirection which is substantially perpendicular to the focusing directionand parallel to a radial direction of the optical disc; moving meansincluding a coil and a magnetic circuits for translating said holdingmeans in the focusing direction and the tracking direction by a drivingforce generated by said coil and said magnetic circuit; and secondsupporting means attached to another side wall of said base forvisco-elastically supporting said magnetic circuit on said base so thatsaid magnetic circuit vibrates at the lowest resonance frequency thereofin the focusing direction, wherein said magnetic circuit is translatedin an opposite direction to the translation direction of said holdingmeans by a driving force acting oppositely to the driving force fortranslating said holding means in the focusing direction.